So-called "piggy-back" transducer mounts have been used both in magnetic and optical disk drives. In such "piggy-back" arrangements, the transducer or lens has its position controlled using a so-called fine actuator. The fine actuator is moveably mounted on a coarse actuator also termed a carriage or headarm. In a preferred arrangement, a servo circuit controls the fine actuator to position the transducer or lens with respect to a record member based upon the position error of the lens or transducer and the desired position with respect to the record member. Either position or velocity profiles may be used in this control. A separate servo circuit controls the coarse actuator to always follow the motions of the fine actuator. A so-called relative position error (RPE) sensor mounted on the coarse actuator measures and indicates the relative displacement of the fine actuator with respect to a reference position on the coarse actuator. The RPE indication is supplied to the servo for the coarse actuator for causing the coarse actuator to follow the motions of the fine actuator. Typically, the responsiveness of the fine actuator is much greater than that of the coarse actuator. This in part is caused by the lower mass of the fine actuator with respect to the mass of the coarse actuator.
During so-called track following operations, the fine actuator follows the desired record track, either magnetic or optical using only minor motions of the fine actuator. During such track following, the coarse actuator generally does not move. During a seek operation wherein the transducer or lens is moved from a current track to a target or desired track, the fine actuator can lead the coarse actuator such that the fine actuator may engage a mechanical stop on the coarse actuator. At this point in time, a seek error can occur resulting in a decreased probability that a target track will be immediately accessed. It is desired to provide controls for ensuring a most rapid seek operation while ensuring that the fine actuator is maintained within a predetermined range of displacements with respect to the coarse actuator.